E.2.1 Implementation-defined pragmas

Ada compilers are allowed to supplement the language-defined pragmas, and
these are a potential source of non-portability. All GNAT-defined pragmas
are described in the GNAT Reference Manual, and these include several that
are specifically intended to correspond to other vendors' Ada 83 pragmas.
For migrating from VADS, the pragma Use_VADS_Size may be useful.
For
compatibility with HP Ada 83, GNAT supplies the pragmas
Extend_System, Ident, Inline_Generic,
Interface_Name, Passive, Suppress_All,
and Volatile.
Other relevant pragmas include External and Link_With.
Some vendor-specific
Ada 83 pragmas (Share_Generic, Subtitle, and Title) are
recognized, thus
avoiding compiler rejection of units that contain such pragmas; they are not
relevant in a GNAT context and hence are not otherwise implemented.